egg yolk, room temperature
tsp lemon juice
tsp dijon mustard
tsp kosher salt
c neutral oil, like safflower or canola
In a medium bowl, whisk together the egg yolk, lemon juice, mustard, salt, and 1 tsp cold water until frothy. Whisking constantly, slowly dribble in the oil until mayonnaise is thick and oil is incorporated. When the mayonnaise emulsifies and starts to thicken, you can add the oil in a thin stream instead of drop by drop.